It has heretofore been known that when paint, printing ink, adhesive or like compositions containing unsaturated compounds which are curable on irradiation with radiation are irradiated with electromagnetic rays, e.g., visible light ray, ultraviolet ray and X-ray, or corpuscular beams, e.g., electron beam, neutron ray and alpha ray, the unsaturated compounds are polymerized and cured. The presence of a polymerization initiator in the compositions markedly increases the rate of polymerization. These techniques are described in, for example, U.S. Pat. Nos. 3,551,235, 3,551,246, 3,551,311 and 3,558,387, Belgian Pat. No. 808,179, and Japanese Patent Application (OPI) No. 110781/74 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Conventional photopolymerizable compositions can provide cured products having excellent flexibility, chemical resistance, wear resistance, luster, adhesion strength, and hue. However, when forming images with such compositions, it is necessary to apply imagewise exposure for a long period of time because the degree of sensitivity of the compositions to irradiation is low. Therefore, when attempting to form fine images, faithful reproduction, i.e., production of high quality images, becomes impossible if even a slight vibration takes place during handling. When using such compositions, it is necessary to increase the amount of irradiation energy from the light source or the corpuscular beam source and, accordingly, the dissipation of a large amount of heat energy should be taken into account. Furthermore, the use of such a large amount of heat energy is liable to cause the deformation or deterioration of the composition coating formed.
Thus various investigations have been carried out in order to overcome the above-described problems by increasing the sensitivity of photopolymerizable compositions.
Japanese Patent Application (OPI) No. 112681/77 discloses light-sensitive compositions comprising photopolymerizable polymers and at least one 3-keto-substituted cumarin sensitizer having the general formula (I) as described hereinafter, or other cumarin sensitizers. In European Pat. No. 0022188, there is disclosed a photopolymerizable composition in which a mixture of a cumarin compound represented by the general formula (I) as described hereinafter and a reducing compound is used as a photopolymerization initiator.
Japanese Patent Application (OPI) No. 107083/74 and Japanese Patent Publication No. 33723/80 disclose photopolymerizable compositions in which, of active halogeno compounds, sulfonyl halide compounds are used in combination with the compounds represented by the general formula (IV): ##STR1## wherein Z is a non-metallic atom group necessary to form a heterocyclic ring containing nitrogen, R.sub.1 is alkyl or substituted alkyl group, and R.sub.2 is alkyl or aryl group.
Furthermore, in Japanese Patent Application (OPI) No. 74887/79 (corresponding to U.S. Pat. No. 4,258,123), there is disclosed a photopolymerizable composition in which the compound represented by the general formula (II) as described hereinafter is used in combination with the compound represented by the general formula (IV).
The sensitivity of these photopolymerizable compositions, however, are not still sufficient.